Transmissible spongiform encephalopathies are believed to be caused by infection with prion pathogens. Prions have some properties in common with other infectious pathogens, but do not appear to contain nucleic acid. Prion proteins accumulate in the central nervous system where they cause neuropathologic changes and neurological dysfunction. Specific examples of transmissible spongiform encephalopathies include but are not limited to scrapie, which affects sheep and goats; bovine spongiform encephalopathy (BSE), which affects cattle; feline spongiform encephalopathy and chronic wasting disease of deer and elk. In humans examples of transmissible spongiform encephalopathies include but are not limited to kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Straüssler-Scheinker Syndrome (GSS), fatal insomnia and variant Creutzfeldt-Jakob disease (vCJD).
Variant Creutzfeldt-Jakob disease recently emerged in humans as an apparent result of the BSE epidemic in Britain and is believed to be caused by the consumption of food products derived from cattle infected with bovine spongiform encephalopathy or “mad cow disease”.
Rendered animal byproducts have commonly been used as protein supplements in animal feed. Rendered animal byproducts are produced from meat byproduct materials that are undesirable for human consumption, such as, for example, bone, connective tissue, skin, hooves, horns, claws, fat, greaves, blood, hair, certain muscles, and combinations thereof. The byproducts are processed, or rendered, to facilitate their addition to the feed.
The emergence and spread of BSE in cattle, beginning in 1986, has been attributed in part to the consumption by livestock of feed containing BSE-contaminated rendered animal byproducts. Most cases have been reported in the United Kingdom. The export of contaminated bovine feed products from the United Kingdom worldwide indicates a possible global presence of BSE and hence the probability of the spread of vCJD. Consistent with these observations is the detection of BSE in most European countries, Japan and Israel. As of April 2002, 125 vCJD cases have been reported worldwide, primarily in the United Kingdom; however, cases have also been reported in Canada, France, Hong Kong, Ireland, Italy, and the United States.
In an effort to prevent, control, and eradicate BSE, several regulatory measures have been put in place worldwide. Many of these regulations prohibit or restrict the use of animal protein and other animal materials in feed. For example, the European Union (“EU”) placed a temporary ban on the use of all processed animal proteins on certain other mammalian materials in ruminant feed. Other EU regulations prohibit the use of mammalian protein in feed, with the exception of milk and milk products, gelatin, hydrolyzed proteins, and non-bovine blood products. In the United States, regulations prohibit the use of mammalian protein in ruminant feed with the exception of milk and blood products, plate waste, and porcine or equine protein that originated from a certified non-ruminant processing facility. In Japan, both mammalian and poultry proteins are prohibited from cattle feed except milk and milk products, gelatin, collagen, and egg and egg products, while fish protein is prohibited unless it is from a certified fish-only processing facility.
Determining compliance with the above legal requirements creates the need for a test to identify the presence of animal proteins and other animal tissue components in feed materials. To assure that these legal requirements can be effectively enforced, tests are needed that can detect mammalian tissue components in concentrations as low as possible. Adequate sensitivity is desired for this purpose.
Being of a structural origin, many of the components of rendered animal byproducts are insoluble and not readily accessible for immunoassay without extensive sample processing. As such, rendered animal products must often be boiled in a salt solution as a means of extracting the reactive component or extensive purification, mainly to remove gelatin, in an attempt to obtain a functional assay. Avoiding this step would be desirable.
What is needed is an assay that overcomes the problems of low reactivity for rendered animal byproducts, thereby maximizing detection.